The invention relates to a switch apparatus for activating switch contacts after a predetermined number of revolutions of a drive shaft which engages at least two cam discs provided with switch points and arranged on camshafts, via gear pinions. The cam discs activate a switch contact when they are in a certain position to each other.
In a previously disclosed switch apparatus, in German DE-AS 23 47 581, the position of the cam discs relative to one another is changed by means of a different number of teeth of its gear pinions. Since the peripheral extent of the teeth is short, the switch period is also short. Thus, there is the risk that the switch period will not be sufficient to effect the switch process reliably. An extension of the switch points in peripheral direction is not possible, as they still partially overlap in two successive revolutions, so that a failure in switching results.
It is the object of the invention to provide a switch apparatus to activate switch contacts after a predetermined number of revolutions of a drive shaft in such a way that the switching can be done reliably, and that the switch period is long enough to have the switch order carried out safely. Such type of apparatus is required, for example, in hoists, finishing machines and the like, in order to effect switching on or off depending upon a distance of travel before reaching terminal stops.
This is achieved by having the camshafts correspond with each other via a transmission gearing, and by having the switch points of both cam discs affect a toggle or rocker lever which may be raised and lowered as well as tilted. The toggle or rocker lever is connected to the switch contacts by means of a thrust rod and, under certain circumstances, a tappet. The slowly revolving cam disc has a rest surface, and the fast revolving cam disc has a switch surface of sufficient length of, perhaps 45.degree. centri-angle to accomplish the switching within the necessary switch period. Only if the toggle lever is kept in switching position by the rest surface and the switch surface simultaneously, can the switching process take place.
After another revolution of the fast revolving cam disc, the rest position of the slowly revolving cam disc is no longer under the toggle lever, which is then only raised on one end by the switch surface of the fast-revolving cam disc, which does not lead to an effective displacement of the switch contacts. The cam discs have limit surfaces, and the toggle lever may have cam followers and be charged by means of a spring towards the cam discs. It presses mainly on the slowly revolving cam disc. When the switch contacts are closed there is an intermediate space between the thrust rod and the tappet of the switch contacts permitting an ineffective pendulum-like swing of the toggle lever with only one side of the lever raised.
The transmission gearing of the switch apparatus meets the requirements and has, for example, a transmission ratio of 20:1. With this difference, it drives the parallel camshafts with the cam discs arranged in alignment with each other. Depending on the structure of the switch arrangement, and according to the requirements, each camshaft may have two or more cam discs arranged coaxially and spaced a distance from each other. The distance is determined by the thickness of the switch elements, taking into consideration intermediate spaces.
An example of the invention is shown in the drawings and explained as follows.